The present invention relates to a rust-preventive composition. More particularly it relates to a rust-preventive composition which is free of the pollution problem, has excellent rust-preventive property and also shows excellent storage stability even when blended in aqueous paints which are expected to grow in demand in future with strengthened legal regulations on use of VOC (volatile organic compounds) and the increasing global interests in the environmental problems.
Hitherto, as rust-preventives, there have been used lead-based pigments such as red lead, lead suboxide, lead cyanamide, calcium plumbate, basic lead sulfate and basic lead chromate; chrome pigments such as zinc chromate, strontium chromate, barium chromate and calcium chromate; phosphate pigments such as zinc phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, phosphites and hypophosphites; molybdate pigments such as zinc molybdate, calcium molybdate, and zinc phosphomolybdate; and borate pigments such as barium metaborate.
In recent years, however, antipollution regulations on use of heavy metal elements such as lead and chromium have been strengthened, and accordingly demand for pollution-free phosphoric acid-based rust-preventives has risen sharply. Especially the rust-preventive compositions comprising aluminum dihydrogen triphosphate, which is a layered phosphate, have excellent rust-preventive performance and are popularly used as a pollution-free rust-preventive containing no heavy metal in various types of paints and coatings such as solvent (non-aqueous) type, aqueous and powder type (Japanese Patent Application Laid-Open (KOKAI) No. 55-160059 (1980)).
However, the rust-preventives comprising the layered phosphate such as aluminum dihydrogen triphosphate have the problem that when they are used for an aqueous paint, storage stability and/or rust-preventive property of the paint may be deteriorated.
Therefore, the rust-preventive compositions blended with the layered phosphate are required to be modified in formulation for improving storage stability of the aqueous paints comprising such compositions. With the technical trend of solvents from the organic type to the aqueous type due to regulations on use of VOC, demand is rising for the development of a rust-preventive composition which shows excellent storage stability when formulated in an aqueous paint.
As a result of extensive studies by the present inventors, it has been found that by using a layered phosphate reacted with ammonia, the obtained composition exhibits excellent storage stability even when formulated in an aqueous paint and also has excellent rust-preventive property. The present invention has been attained on the basis of this finding.